Chucks are used for holding substrates in process chambers, and are generally of three types: mechanical, vacuum, and electrostatic chucks. Electrostatic chuck is a mechanism for holding a substrate (wafer) using electrostatic attraction forces used in vacuum chambers. Through the generation of an electric field between wafer and supporting chuck, an attractive force is exerted on the wafer. The force is distributed homogenously over the surface, can be switched on/off and adjusted electrically. It ensures flat wafer adherence to the support as well as good thermal contact.
FIG. 1A illustrates the basic design of a conventional electrostatic chuck 10. It includes a three-layer structure formed by a chuck body. (or substrate) 12 made of a dielectric material (typically Ceramics), carrying an electrically conductive layer 14 containing an electrode arrangement defining one or two pairs of electrodes (not shown), and a top dielectric layer 16 (any dielectric material can be used, such as ceramics, plastics, etc, and even vacuum). Structure 10 closely resembles that of a parallel plate capacitor generating an electrostatic force that enables to flat silicon wafer structure W. Also, high acceleration motion systems can be used for wafer navigation. By applying a voltage between the two electrode plates, the wafer is attracted to the chuck. The generated electrostatic force is also affected by the thickness of dielectric film 16, the relative dielectric constant of the film material, as well as the chuck area. This is expressed by the following relation:
                    F        =                                            A              ·                              ɛ                0                            ·                              ɛ                R                2                                      2                    ·                                    [                              V                d                            ]                        2                                              (        1        )            wherein F is the chucking force [N], A is the effective chucking area [m2]; ∈0 is 8.85e-12F/m—absolute permittivity of vacuum; ∈R is the dielectric constant of the chosen material; V is the potential difference between the electrode and the substrate [Volts]; and d is the thickness of the upper dielectric layer.
FIG. 1B shows the typical process of manufacturing such a conventional chuck structure 10. The main structure (chuck body) 12 is prepared. Thin conductive layer 14 is deposited on top of structure 12. A planarization process (mechanical lapping) is applied to layer 14 to flat the top surface thereof. Then, thin dielectric layer 16 is deposited on top of conductive layer 14 and a further mechanical lapping is applied to layer 16 for lapping and polishing its top surface.
Conventional chucks can also be appropriately designed to support wafers of different diameters. To this end, the electrically conductive layer is appropriately patterned to define different electrode pairs.